The invention relates to a bus communication system as described in the precharacterizing part of claim 1. A USB (Universal Communication Bus) system is an example of such a communication bus system. The USB system provides for detection of devices connected to the bus. A USB master station, for example a PC, contains a resistor connected between a communication line and ground. A peripheral station, for example a display monitor, contains a resistor connected between the communication line and a power supply terminal.
Thus, when the peripheral station is connected to the communication line, the potential of the communication line will be pulled towards the level of the potential on the power supply terminal. When the peripheral station is not connected to the communication line or when it is switched off, the potential of the communication line will remain at ground level. The master station monitors the potential of the bus line before it starts communication. If the potential is at or near ground level, the master station concludes that no active peripheral station is connected to the communication line and the master station does not start communication. If the master station detects that the potential of the communication line is more than a threshold away from the ground level, the master station concludes that an active peripheral station is connected to the bus and the master station will start communication if desired.
When the peripheral station is switched-on it will preferably execute an initialization program. It is desirable that during execution of this initialization program no communication occurs via the communication line. In principle this can be realized by executing the initialization program very quickly so that initialization is complete before the master station can respond to detection of the peripheral station, but this places severe restraints on the speed of the peripheral station.